[ANSI-Smalltalk] Re: A list of interesting methods, ifNotNil:

[Richard Sargent]

Paolo Bonzini bonzini at gnu.org wrote:

>> x ifEmpty: block1 ifNotEmptyDo: block2
>> 
>> And I say *could*, I'm not endorsing this particular addition -- I'm
>> just using to show why IMO using the "do" suffix to choose between zero-
>> and one-arity blocks is bad.

 

A while ago, I had occasion to implement something like this. I guess you
could call it a reification of the "0, 1, infinity" rule that P. J. Plauger
described in Software Development or some other magazine nearly 20 years
ago.


zeroDo: emptyHandler oneDo: singularHandler multipleDo: multipleHandler
	"Answer the result of evaluating the appropriate handler for the
cardinality of the receiver.
	 Each handler is a Block.
	 The emptyHandler takes no arguments.
	 The singularHandler takes an optional argument, the single element
of the collection.
	 The multipleHandler takes an optional argument, the collection
itself."

	self isEmpty ifTrue: [^emptyHandler value].
	self isMultiple ifTrue: [^multipleHandler valueWithOptionalArgument:
self].
	^singularHandler valueWithOptionalArgument: self asArray first


Richard Sargent
rsargent at 5x5.on.ca
http://www.pendragonfarm.com/